Jonathan A. Jones
I describe the use of techniques based on composite rotations to develop controlled phase gates in which the effects of weak Ising couplings are suppressed. A tailored composite phase gate is described which both suppresses weak couplings and is relatively insensitive to systematic errors in the size of strong couplings.
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In the nonadiabatic dynamics across a quantum phase transition, the Kibble-Zurek mechanism predicts that the formation of topological defects is suppressed as a universal power law with the quench time. In inhomogeneous systems, the critical point is reached locally and causality reduces the effective system size for defect formation to regions where the velocity of the critical front is slower than the sound velocity, favoring adiabatic dynamics. The reduced density of excitations exhibits a much steeper dependence on the quench rate and is also described by a universal power-law, that we dem…
Quantum systems interacting with environments tend to have their information lost from transmission through the correlations generated with the degrees of freedom of the environment. For situations where we have non- Markovian environments, the information contained in the environment may return to the system and such effect can be captured by non-Markovian witnesses. In the present work, we use a central qubit coupled to a spin chain with Ising interactions subject to a magnetic field, i.e., a central spin model, and solve the exact dynamics of a system subject to dephasing dynamics via Kraus…
We study quantum correlations in an isotropic Ising ring under the effects of a transverse magnetic field. After characterizing the behavior of two-spin quantum correlations, we extend our analysis to global properties of the ring, using a figure of merit for quantum correlations that shows enough sensitivity to reveal the drastic changes in the properties of the system at criticality. This opens up the possibility to relate statistical properties of quantum many-body systems to suitably tailored measures of quantum correlations that capture features going far beyond standard quantum entanglem…
Adiabatic quantum computing is an analog quantum computing scheme with various applications in solving optimization problems. In the parity picture of quantum optimization, the problem is encoded in local fields that act on qubits which are connected via local 4-body terms. We present an implementation of a parity annealer with Transmon qubits with a specifically tailored Ising interaction from Josephson ring modulators.
The measured multi-dimensional spectral response of different light harvesting complexes exhibits oscillatory features which suggest an underlying coherent energy transfer. However, making this inference rigorous is challenging due to the difficulty of isolating excited state coherences in highly congested spectra. In this work, we provide a coherent control scheme that suppresses ground state coherences, thus making rephasing spectra dominated by excited state coherences. We provide a benchmark for the scheme using a model dimeric system and numerically exact methods to analyze the spectral r…
We demonstrate that the performance of a quantum annealer on hard random Ising optimization problems can be substantially improved using quantum annealing correction (QAC). Our error correction strategy is tailored to the D-Wave Two device. We find that QAC provides a statistically significant enhancement in the performance of the device over a classical repetition code, improving as a function of problem size as well as hardness. Moreover, QAC provides a mechanism for overcoming the precision limit of the device, in addition to correcting calibration errors. Performance is robust even to miss…
Suppressing Intrinsic Spin-Phonon Errors in Trapped-Ion Quantum Simulation
通过帧变换序列，在保持可编程伊辛耦合的同时，抑制离子阱量子模拟中由声子中介相互作用引起的本征自旋-声子误差，实现数量级更低的误差。
Suppressing excitations using quantum-Brachistochrone and nearest-neighbour interactions
针对传统反绝热协议抑制量子激发需复杂多体项的问题，提出对TFIM已有耦合项做局域含时调制的方法，可提升保真度与抗噪性，还解析证明了反Kibble-Zurek标度，为简易抗噪量子态制备提供新思路。
Error suppression by a virtual two-qubit gate
本研究提出利用虚拟双量子比特门（VTQG）抑制超导量子计算机中SWAP门引入的误差，通过减少SWAP门数量并结合脉冲高效编译，在8量子比特横场伊辛模型模拟中实现一个数量级的精度提升。
We study a quantum Ising chain with tailored bulk dissipation, which can be mapped onto a non-Hermitian Ashkin-Teller model. By exploiting the Kohmoto-den Nijs-Kadanoff transformation, we further map it to a staggered XXZ spin chain with pure-imaginary anisotropy parameters. This allows us to study the eigenstates of the original Liouvillian in great detail. We show that the steady state in each parity sector is a completely mixed state. The uniqueness of each is proved rigorously. We then study the decay modes on the self-dual line corresponding to the uniform XXZ chain and obtain an exact fo…
Performance of a Quantum Annealer for Ising Ground State Computations on Chimera Graphs
针对Chimera图上的Ising模型，采用分支切割和半定规划算法求得可证明最优解，并与D-Wave 2000Q量子退火器的解进行比较，评估其解的质量。
Problem-tailored Simulation of Energy Transport on Noisy Quantum Computers
针对量子计算机资源限制问题，提出面向问题定制的策略，在量子硬件上模拟混合场伊辛链的无限温度能量输运，通过泡利Y基采样和重整化策略提升效率与准确性，还扩展了方法适用性并提出变分基搜索方法。
Optimal performance of thermal machines is reached by suppressing friction. Friction in quantum thermodynamics results from fast driving schemes that generate nonadiabatic excitations. The far-from-equilibrium dynamics of quantum devices can be tailored by shortcuts to adiabaticity to suppress quantum friction. We experimentally demonstrate friction-free superadiabatic strokes with a trapped unitary Fermi gas as a working substance and establish the equivalence between the superadiabatic mean work and its adiabatic value.
Geometrical scheduling of adiabatic control without information of energy spectra
提出一种无需能谱信息的量子绝热最短时间路径协议，利用反绝热驱动设计参数调度，在横向场伊辛链和轴向次近邻伊辛模型上验证了其有效性。
We propose that weak continuous probing may be exploited to determine and define quantum phases of complex many-body systems based on the measurement record alone. We test the resulting phase criterion in numerical simulations of measurements on the Bose-Hubbard model and the quantum Ising chain. This yields a phase transition point in reasonable agreement with the quantum phase transition in the ground state of the closed system in the thermodynamic limit, despite the system being highly excited through the measurement dynamics. At high measurement strengths, the system's response enters a Ze…
A mixed-integer linear programming (MILP) formulation is presented for parameter estimation of the Potts model. Two algorithms are developed; the first method estimates the parameters such that the set of ground states replicate the user-prescribed data set; the second method allows the user to prescribe the ground states multiplicity. In both instances, the optimization process ensures that the bandgap is maximized. Consequently, the model parameter efficiently describes the user data for a broad range of temperatures. This is useful in the development of energy-based graph models to be simul…
We show that dynamic quantum phase transitions (DQPT) in many situations involve renormalization group (RG) fixed points that are unphysical in the context of thermal phase transitions. In such cases, boundary conditions are shown to become relevant to the extent of even completely suppressing the bulk transitions. We establish these by performing exact RG analysis of the quantum Ising model on scale-invariant lattices of different dimensions, and by analyzing the zeros of the Loschmidt amplitude. Further corroboration of boundaries affecting the bulk transition comes from the three-state quan…
Traversing Quantum Control Robustness Landscapes: A New Paradigm for Quantum Gate Engineering
本文提出QCRL框架与RIPV算法，通过在鲁棒性水平集间变换脉冲，实现从任意鲁棒门配置出发构造抗噪量子门。
Color it, Code it, Cancel it: k-local dynamical decoupling from classical additive codes
本文提出一种基于图着色和经典编码理论的动态解耦序列设计框架，通过高效消除特定局部相互作用，实现紧凑且硬件定制化的量子控制序列，应用于量子计算与模拟。
Exact results on finite size corrections for surface codes tailored to biased noise
本文研究偏置噪声下 XY 与 XZZX 表面码，在特殊无序点获得任意奇数码距的精确逻辑失败率，并揭示有限尺寸修正导致阈值提取偏差，提出分通道阈值估计方法。
We utilize machine learning models which are based on recurrent neural networks to optimize dynamical decoupling (DD) sequences. DD is a relatively simple technique for suppressing the errors in quantum memory for certain noise models. In numerical simulations, we show that with minimum use of prior knowledge and starting from random sequences, the models are able to improve over time and eventually output DD-sequences with performance better than that of the well known DD-families. Furthermore, our algorithm is easy to implement in experiments to find solutions tailored to the specific hardwa…
Quest for quantum advantage: Monte Carlo wave-function simulations of the Coherent Ising Machine
本文使用蒙特卡罗波函数方法模拟相干伊辛机在强量子机制下的性能，通过初始量子叠加和纠缠降低耗散，实现更快的成功概率提升，并证明量子隧穿效应可避免陷入假极小，展示量子优势潜力。
Detecting quantum phase transitions via shallow variational quantum circuits
研究通过浅变分量子电路检测量子相变，利用变分量子本征求解器的Delta-VQE方法，经对含三自旋团簇相互作用的一维横场伊辛模型研究发现，其诊断能力依赖于合理选择有物理代表性的近似，能高效探测量子临界性。
Quantum Correlations and Entanglement in Generalized Dicke-Ising Models
研究广义迪克-ising模型中量子关联与纠缠的特性，通过光与物质的强耦合探索超辐射模式，发现长程序序和磁子对的出现，以及光场对量子纠缠优化的作用。
High-connectivity circuits are a major roadblock for current quantum hardware. We propose a hybrid classical-quantum algorithm to simulate such circuits without swap-gate ladders. As main technical tool, we introduce quantum-classical-quantum interfaces. These replace an experimentally problematic gate (e.g. a long-range one) by single-qubit random measurements followed by state-preparations sampled according to a classical quasi-probability simulation of the noiseless gate. Each interface introduces a multiplicative statistical overhead which is remarkably independent of the on-chip qubit dis…
Suppression of Universal Errors in DFS-Encoded Superconducting Geometric Logical \emph{T} Gate
本文提出一种超导几何逻辑T门方案，通过整合去相干自由子空间编码与多环优化复合几何脉冲工程，实现对通用误差的高阶抑制，提升了对多种噪声源的鲁棒性。
The D-Wave quantum annealers make it possible to obtain high quality solutions of NP-hard problems by mapping a problem in a QUBO (quadratic unconstrained binary optimization) or Ising form to the physical qubit connectivity structure on the D-Wave chip. However, the latter is restricted in that only a fraction of all pairwise couplers between physical qubits exists. Modeling the connectivity structure of a given problem instance thus necessitates the computation of a minor embedding of the variables in the problem specification onto the logical qubits, which consist of several physical qubits…
Neutral atom array serves as an ideal platform to study the quantum logic gates, where intense efforts have been devoted to improve the two-qubit gate fidelity. We report our recent findings in constructing a different type of two-qubit controlled-PHASE quantum gate protocol with neutral atoms enabled by Rydberg blockade, which aims at both robustness and high-fidelity. It relies upon modulated driving pulse with specially tailored smooth waveform to gain appropriate phase accumulations for quantum gates. The major features include finishing gate operation within a single pulse, not necessaril…
Quantum computing crucially relies on the ability to efficiently characterize the quantum states output by quantum hardware. Conventional methods which probe these states through direct measurements and classically computed correlations become computationally expensive when increasing the system size. Quantum neural networks tailored to recognize specific features of quantum states by combining unitary operations, measurements and feedforward promise to require fewer measurements and to tolerate errors. Here, we realize a quantum convolutional neural network (QCNN) on a 7-qubit superconducting…
Counterdiabatic Driving with Performance Guarantees
针对反绝热驱动缺乏性能保证或计算困难的问题，提出一种非变分、与系统无关且指数收敛的CD展开方法，结合有限时间绝热协议扩展至热力学极限，数值证明其优于现有变分方法。
Shot-noise reduction for lattice Hamiltonians
提出一种基于几何划分的测量策略，通过局部本征基测量降低能量估计方差，从而减少量子晶格系统能量期望值估计所需的测量次数。
Ever since the insight spreaded that tailored dissipation can be employed to control quantum systems and drive them towards pure states, the field of non-equilibrium quantum mechanics gained remarkable momentum. So far research focussed on emergent phenomena caused by the interplay and competition of unitary Hamiltonian and dissipative Markovian dynamics. In this manuscript we zero in on a so far rather understudied aspect of open quantum systems and non-equilibrium physics, namely the utilization of purely dissipative couplings to explore pure quantum phases and non-equilibrium phase transiti…
Superstrong Dynamics and Directional Emission of a Giant Atom in a Structured Bath
本研究通过将transmon量子比特非局域耦合到高阻抗耦合腔阵列实现结构化光子环境中的巨型原子，达到超强耦合区，观测到多模相互作用，并利用破缺对称性实现定向光子发射，为多模光物相互作用调控提供新方案。
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